1. Field of Invention
The present invention relates to a method of fabrication a barrier layer. More particularly, the present invention relates to a method of fabrication a barrier layer that can enhance the adhesion of a via with low-k dielectric sidewalls.
2. Description of Related Art
In general, as the level of integration of integrated circuits increases, the number of metal interconnects necessary for interconnecting devices increases correspondingly. This is especially true in the fabrication of deep sub-micron VLSI circuits. One important and highly desirable property of metallic interconnects is a good electrical conductivity even when the contact area is very small. At present, the most common material for forming metallic interconnects is aluminum. However, copper has a lower resistance and a higher melting point. Therefore, as the level of integration continues to increase, copper has the potential to replace aluminum as a material for forming interconnects in the generation to come despite the many foreseeable problems that still exist.
FIG. 1 is a cross sectional diagram showing a conventional barrier layer structure. As shown in FIG. 1, the barrier layer structure is formed by first providing a semiconductor substrate 10, wherein a conductive layer 11 such as a metallic line structure has already been formed above the substrate 10. Then, a dielectric layer 12 is formed over the conductive layer 11 and the substrate 10. The dielectric layer 12 can be formed using a low-k dielectric material. Next, a via 14 is formed in the dielectric layer 12, and then a highly conductive material such as tungsten, copper or aluminum is deposited into the via 14. In general, a barrier layer is also formed between the via 14 and the conductive layer and between the via 14 and the dielectric layer 12. The reason for forming the barrier layer 13 is to increase adhesion of conductive material onto the sides of the vial 4 as well as to prevent the diffusion of conductive material into the dielectric layer. Nowadays, the most commonly used barrier layer materials include titanium/titanium nitride (Ti/TiN), tungsten nitride (WN),tantalum (Ta) and tantalum nitride (TaN).
FIG. 2 is a cross-sectional view showing a conventional barrier layer structure formed by a damascene process. As shown in FIG. 2, the barrier layer structure is formed by first providing a semiconductor substrate 20 having a conductive layer 21 formed thereon. The conductive layer can be a first metallic line structure, for example. Next, a dielectric layer 22 is formed over the conductive layer 21 and substrate 20. The dielectric layer 22 can be formed using a low-k dielectric material. Thereafter, a second opening 24 and a first opening 23 are sequentially formed in the dielectric layer 22. Subsequently, a barrier layer 25 is formed over the first opening 23 and the second opening 24. In general, the most common used barrier layer materials include titanium/titanium nitride (Ti/TiN), tungsten nitride (WN), tantalum (Ta) and tantalum nitride (TaN). The reason for having a barrier layer 13 is to increase the adhesive strength of subsequently deposited conductive material as well as to prevent the diffusion of conductive material to the dielectric layer. In the subsequent step, a conductive layer 26 is deposited into the openings 23 and 24 and over the dielectric layer 22. The conductive layer 26 can be formed using a material that has good electrical conductivity, for example, tungsten, copper or aluminum. Finally, the conductive layer 26 is planarized using a chemical-mechanical polishing (CMP) operation to complete the damascene fabricating process. The advantage of using a damascene process includes its capacity for forming both a via and a second metallic line structure in the same processing operation. For example, a via structure is formed in the first opening 23 and a second metallic line structure is formed in the second opening 24.
The aforementioned methods of fabricating a barrier layer do have defects. First, if the material used for filling the via is copper (future trend), since cross-diffusion between copper and dielectric material is very strong, a barrier formed using conventional material and method cannot prevent diffusion. Organic low-k dielectric material is often used as a dielectric layer but the organic low-k dielectric material has poor adhesion with a conventional barrier layer material. This is because a low-k dielectric material has a high moisture absorption capacity; this is especially true for an organic low-k dielectric material. Therefore, a layer of moisture will be retained on the surface layer of the dielectric material. Hence, the dielectric layer can provide only poor adhesion with the subsequently deposited barrier layer and conductive layer.
In light of the foregoing, there is a need to provide a method of fabrication a barrier layer.